Before you leave org you need copies of all the policies about maternity policy, redundancy etc...
Also you need to have all the documentation around the grievance.
I was compromised out of my job earlier this year, face didn't fit, in UK as someone has said there is a legal requirement for you to see a solicitor some of it paid by the company my company paid £300 - I had a further solicitors bill of £990 - but she argued and got me an extra £8K so well worth it!
Part of the discussions with my solicitor included them having to explain they are taking away your right to sue etc..., I spoke to my solicitor about not taking the package and going through tribunal (want to avoid but if I had a better case then I was kinda willing!) - she advised me that often courts will look at people that have walked away from a compromise and not tried to resolve and may not award in your favour. Basically the courts want companies and employees to come to agreements.
My package increase was based on they were trying to get rid of me but not others in my team a huge headcount program was going on but I didn't met the critriea to be going... and I had been Tupe'd in just under a year over, whilst on Maternity leave so it was very very dodgy!
That said I've not yet been able to get a job, part of your arguement would be you would be unable to start another role at your stage of pregnancy and get maternity benefits and the unfair selection side of things.
You have the right to see the selection criteria, how it was applied, in interview they can show you the scores of all of you and not the names etc...
A manager many years ago of mine wanted rid of one of my team and I had to do the dirty work, even though I didn't agree with it, (Luckly HR agreed with me!), but if I had to have gone through with it I would have had to show no emotion or show that I was not happy about the situation, so maybe the manager is in a difficult position (just saying incase it is relevant you don't know for sure - treat everyone you deal with throughout with professionalism so you don't get any grief/issues after).
I've been a witness in a tribunal and they are horrid, so if it comes down to the fact you appeal the decision, you need to make sure they have followed the process 100% - if they have messed their own process up one bit your first appeal is based on that and you ask for the process to be re-done correctly.
This is a time delaying tactic....
If they have done it correctly then you appeal on the grounds of appeal but before that ask for the selection markings/interview notes and where you failed to pass. Ask for the feedback on the interview and what you should have done to pass...
Good luck it is a shitty position to be in and it hurts when it feels personal.
Good luck with the baby as well xxx